David Chandler, a young science writer for Boston magazine, examines the evidence for life on Mars and lo, finds it good. The evidence varies, however. There are, of course, the ""not proven"" judgments based on the three biological experiments included aboard the Viking landers. Here the case for microbial life is sufficiently tantalizing to convince a Jastrow or a Sagan, but not some hard-nosed chemists who reason that nonorganic processes could account for the results. Chandler presents both sides, with obvious sympathy for the pro-lifers. As he proceeds in his bio defense, the arguments grow more diffuse and tenuous. He endorses the ""wave of darkness"" theory as evidence of vegetation, although others have discounted this as an anomaly of observation. When he quotes Jacques Monod's arguments of ""repetition and regularity"" as indicative of intelligent life to support the idea that colossal pyramids at a site called Elysium might really be the red planet's counterpart of Egypt or Peru, we draw the line. All the same, the writing is intelligent, while the preliminaries on terrestrial evolution and the assessment of how best to settle the issue through further explorations--modestly through ""rovers"" and more extravagantly by astronaut explorers--have a decided appeal.